The present invention relates to a cathode ray tube (CRT) and more particularly, to a cathode ray tube capable of reducing the power consumption and preventing deflection magnetic fields from leaking to the outside of the cathode ray tube.
A CRT is a device for displaying an image on a screen by vertically and horizontally deflecting electron beams generated from an electron gun and landing the deflected electron beams onto the phosphor layers formed on the screen. The deflection of the electron beam is controlled by a deflection yoke mounted on an exterior surface of a funnel of the CRT and which forms vertical and horizontal magnetic fields. The CRTs are generally employed for color televisions (TVs), monitors and high definition televisions (HDTV). And with the increasing use of CRTs, there is a need to reduce the length of the CRT for increasing brightness of the displayed image and for reducing the size of the final products, such as TVs, monitors and HDTVs.
When reducing the length of the CRT, the electron beams should be deflected with wide-angles, and the deflection frequency and current supplied to the deflection yoke should be increased for wide-angle deflections of the electron beams. As the deflection frequency and current increases, the deflection magnetic field tends to leak to the outside of the cathode ray tube and the power consumption increases.
In order to decrease the magnetic field leakage, a compensation coil is generally mounted with the deflection yoke. When, however, the compensation coil is employed, the power consumption of the cathode ray tube increases. Alternatively, in order to decrease the deflection power and the magnetic field leakage at the same time, it is conventionally preferable to decrease the neck diameter of the cathode ray tube and the outer diameter of the funnel near the neck side on which the deflection yoke is mounted, so that the deflection field efficiently acts on the electron beams. However, when the neck diameter is simply decreased, there are some disadvantages including the resolution of the image deteriorating due to the reduced diameter of the electron gun, and the outer electron beams tending to bombard the inner wall of the funnel, thus results in that the bombarded electron beams are not properly landed on the phosphor layer of the screen.
In order to solve these problems, U.S. Pat. No. 3,731,129 discloses a funnel having a wider peripheral portion sealed to the periphery of the panel, and a deflection portion whose cross-sectional configuration gradually varies, from a rectangular shape substantially similar to that of the rectangular image produced on the panel to a circular shape. Thereby, the vertical and horizontal coils of the deflection yoke are more proximately located to the passage of the electron beams, and deflect the electron beams with reduced deflection power and without bombarding the electron beams to the inner wall of the funnel.
However, if the funnel having rectangular cross-section is designed without precisely considering the passage of the electron beams, the deflection magnetic fields generated by the deflection yoke cannot effectively deflect the electron beams, and the power consumption and the deflection magnetic field leakage cannot be minimized.
To overcome these shortcomings, Japanese Laid Open Patent 9-320492 discloses a funnel, whose cross-section of the exterior surface at the neck side changes from a circular shape to a non-circular shape which has a maximum diameter along a direction (diagonal direction) other than the horizontal axis and the vertical axis. The angle between the diagonal direction and the horizontal axis changes according to the distance from the electron gun. The Japanese Patent discloses that the CRT having such funnel can reduce the deflection power and the magnetic field leakage by mounting the deflection yoke at the position nearest to the passages of the electron beams.
However, the exterior shape of the funnel on which the deflection yoke is mounted is designed without precisely considering the passages of the electron beams and the S-value (i.e., the distance between the holes of the electron gun through which the electron beams pass) by which the convergence and focusing characteristics of the electron beams are changed.
Accordingly, an embodiment of the present invention is directed to a cathode ray tube which substantially obviates one or more of the problems due to the limitations and disadvantages of the related art.
An object of an embodiment of the present invention is to provide a cathode ray tube capable of minimizing the power consumption and preventing deflection magnetic fields from leaking to the outside of the cathode ray tube.
Another object of an embodiment of the present invention is to provide a cathode ray tube having a funnel whose exterior surface is designed similar to the passage of the electron beams.
Further object of an embodiment of the present invention is to provide a cathode ray tube particularly suitable for flat-panel cathode ray tube.
To accomplish these and other advantages, an embodiment of the cathode ray tube of the present invention includes a rectangular panel on which a phosphor screen is formed, a neck in which an electron gun assembly for emitting three electron beams is disposed and a funnel. The funnel which is comprised of a body portion and cone portion wherein a contour of the cross-section of said cone portion is a non-circular shape and the perpendicular distance from the tube axis to the contour occurs in the substantially diagonal direction which makes an angle xcex8 with respect to the horizontal axis according to the following inequality xcex8xe2x88x92(4.3+(S/3.8)) less than xcex8xe2x80x2 less than xcex8+(4.3+(S/3.8)) wherein xcex8 is the angle in degree the diagonal of the face panel makes with respect to the horizontal axis; S is the distance in mm between the centers of the electron passing holes of the electron gun assembly.
The objectives and other advantages of the present invention will be realized and attained by the structure particularly pointed out in the written description and claims as well as the appended drawings. It is also to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.